This invention generally relates to testing electronic devices, and more particularly relates to parametric testing of electronic devices such as integrated circuits.
As is well known, parametric test units are used to test electronic devices such as integrated circuits for parameters such as current and voltage. In particular, a "per-pin" parametric test unit is connected to a single pin or terminal of an electronic device. As an example, the pin of the device might be internally connected to an electrode of a transistor to be tested. Parametric test units have been used to force a predetermined voltage on a test device pin, and concurrently measure the current drawn by that pin. Alternatively, parametric test units have been used to force a predetermined current into a test device pin, and concurrently measure the voltage at the pin. These two functions or modes of testing have been descriptively referred to as force voltage/measure current and force current/measure voltage. Parametric measurements relating to voltage and current are correlated to provide important information regarding the quality of the device under test.
It has also been well known that while keeping the pin voltage in a predetermined range such as -5 volts to +15 volts, it is desirable to be able to maximize the current that is measured or forced into the device under test to optimize the accuracy of the parametric testing. Typically, the current is measured across or forced through a resistor, and a plurality of parallel connected range resistors have been used. In order to change from one range resistor having a predetermined precision resistance to another range resistor having a different predetermined precision resistance, corresponding relays have been placed in series with the resistors. In operation, only one relay is activated at a time, and its corresponding range resistor is selectively switched into the parametric test circuit.